The current trend of using packet networks (PN) to transport data traditionally carried over circuit switched networks such as the Public Switched Telephone Network (PSTN) has created a need to support the installed-base of terminals attached to the PSTN. FIG. 1 illustrates a traditional PSTN environment as well as the interlace to a PN substitute network, as may be used with various customer premise equipment, such as telephones, fax machines, and modems.
The different nature between the two types of networks may be related to different operating characteristics such as bandwidth, delay, variations in delay, and loss of information, e.g., packet loss. The differences in characteristics between these networks can affect the terminals that have been designed with PSTN characteristics in mind, if and when those terminals need to communicate over a packet network. For example, many terminals are delay sensitive, and their interactive behavior with other components has been designed in consideration of the delay characteristics of the network in use at the time of their inception, typically, the PSTN. Further, it should also be appreciated that data communication networks need not exclusively include a packet network or a PSTN. For example, future networks may include portions of their infrastructure provided by one or the other type of network, as depicted in FIG. 2.
Hence, there is a need for the ubiquitous support of the installed-base of terminals on both networks. This support may involve the providing of new mechanisms to facilitate the communication of traditional devices over packet networks. Support for these devices can depend on several factors, including the transported media characteristics, and thus can dictate the needs for a real-time infrastructure, such as voice communications, versus a non-real-time infrastructure, such as fax communications. Further, support for these devices can dictate the needs for a transparent support mode, i.e., one by which the actual data is transported transparently over the existing voice packet network infrastructure, versus a demodulation/remodulation support mode, where the information is demodulated, transported, and then remodulated.
As described above, the transport of data over a packet network may be subject to variation of delay, also known as jitter, as well as to packet loss characteristics, for example, during the establishment of a communication session, or during actual data transfer. Further, at the end of a communication session, once a terminal device decides to terminate a communication session, problems can occur in the tearing down of any remaining communication links. Accordingly, although some support mechanisms have been devised recently for the transport of voice and fax communications, a strong need exists for resolving various other issues relating to modem communication sessions, such as those related to the call numbering, establishment, transport and termination features.